Tuberculosis is a disease that rennains a nnajor thireat to global public health. The severity of the epidemic has been intensified by the frequency of coinfection with HIV in developing nations and the emergence of multidrug resistant strains. Novel approaches to stimulate a more protective immune response are of particular interest to combat the increase in drug resistant strains. Our long-term objective is to understand the involvement of interleukin (IL)-12 and IL-27 in human macrophage responses and the impact of these responses on the complete immune response during tuberculosis. The major hypothesis to be investigated in this proposal is that autocrine/paracrine response to IL-27 impedes macrophage effector functions that control growth of M. tuberculosis. Oui- preliminary results have indicated that when IL-27 is neutralized during infection of IL-12-treated macrophages, there is a significant reduction in mycobacterial recovery. Consistent with control of mycobacterial growth is elevated production of interferon (IFN)-D and TNF-D by infected macrophages treated with IL-12 and a soluble receptor to neutralize IL-27. The first aim utilizes molecular approaches to identify important cytokines and test the hypothesis that tumor necrosis factor and IFN-D are indispensable to this mechanism. The second specific aim investigates the consequences of IL- 12 treatment and neutralization of IL-27 on macrophage effector functions. The rationale involved is that IFN-D produced as a result of this treatment promotes a toxic intracellular environment that hinders mycobacterial growth. The work described in this aim investigates the involvement of nitric oxide in the macrophage response during infection and examines progression ofthe mycobacterial phagosome within the endosomal pathway. The third specific aim tests the hypothesis that novel mechanisms operate to control transcription of IL-27 EBI3 and p28 genes. Since IL-27 is involved in host responses to a number of chronic infections and disease states, including tuberculosis, it is important to understand the molecular mechanisms that regulate IL-27 gene expression. We have proposed basic research into host immune responses during infection that could have implications in design of therapeutic strategies and vaccines.